Attempts will be made to further elucidate the phenomenon of transovarial transmission of LaCrosse encephalitis virus in the mosquito, Aedes triseriatus; including whether the capacity for transovarial transmission is restricted to only certain A. triseriatus populations, which might help explain the discontinuous distribution of endemic foci of the virus; whether transovarially-infected males can transmit the virus to females via insemination; and whether the virus may be transmitted via nectar feeding of the mosquitoes. To help determine how broadly transovarial transmission occurs within the California encephalitis virus group, attempts will be made to transmit Trivittatus virus transovarially in the mosquito, Aedes trivittatus. Attempts will be made to determine: the effect of sequential mouse brain passages and continuous colonization of LaCrosse virus and A. triseriatus, respectively, on the infection and transmission rates observed; the site of the barrier mechanism that prevents transmission of LaCrosse virus by infected Aedes hendersoni; and the capability of A. hendersoni - A. triseriatus hybrids for transmission of LaCrosse virus. Methods of suppressing A. triseriatus populations will be explored with emphasis on finding ways to augment the competitive success of the non-vector, A. hendersoni, versus the vector, A. triseriatus.